The present invention relates generally to welding apparatus and more particularly to methods and apparatus for welding various battery components, specifically battery terminal connectors to electrode grid/plates where the battery components are made from lead. Subject matter of this application is related to co-pending application Ser. No. 954,485, filed Oct. 25, 1978, filed simultaneous herewith and assigned to the same assignee as this application.
In the relatively recent past, there has been an increasing trend towards making a greater variety of rechargeable electrolytic power cells in the more commercial sizes such as D-size (or "flashlight size") batteries. This has been particularly true in the case of one of the most common secondary cells-the lead-acid battery. The principal battery constituents in such cells include the positive plate and the negative plate (both usually in the form of expanded metal grids), porous separators located between the plates and an electrolyte.
The plates, with the separators located on each side thereof, are rolled up into a wound battery cell core. The cell core and the electrolyte are then placed in a suitable container which is eventually sealed closed with a top. The electrode grids are usually formed with small tab portions protruding up from the top of the wound cell core for ultimate connection to a battery terminal on the finished battery.
In lead-acid cells, both electrode grids are made from lead as are terminal connectors which electrically coupled each grid to its corresponding battery terminal. Because the components are made of lead, they are relatively easy to weld together since lead has such a low melting point. However, the low melting point can also be the source of problems because of the electrode grids than solid. If the tabs were exposed to an excessive amount of heat, the portions of the tabs, which are directly connected to the grids, might be melted, either completely separating the tab from its corresponding electrode grid or so weakening the connection as to carry only a very small current. The cell would thus be rendered useless, or at least weakened even if only one tab were so separated.
During the welding, portions of the tab could also melt and drop down to the cell core and possibly couple the two oppositely-poled electrode grids together. Similarly, the heat might even be sufficient to fuse small portions of the two different electrode grids together. In either event, the cell would have an inherent short circuit and would be rendered useless. Therefore, it is important, particularly in welding lead battery components, to provide sufficient heat for welding the lead yet prevent complete destruction or even partial deterioration of the the connective tab portion as well as dripping of molten lead.
One prior art patent, U.S. Pat. No. 3,873,803 issued to Young et al., has suggested using an electrode head for laterally moving the torch "flame" of an arc welding apparatus to weld posts members to a cell core. Although this approach has provided satisfactory results in certain respects, the cell pack (or core) must be physically moved simultaneously with the torch "flame" while the components are being welded. Thus, additional apparatus is required for effecting such movement, but if carried out by hand there is a danger that the target will be exposed to the heat for too long, thereby rendering the welding process susceptible to the foregoing drawbacks. In addition, there is no convenient means for automatically retaining the terminal connector in place during the welding operation.
Accordingly, it is an object of the present invention to provide new and improved process steps and apparatus for welding small battery components particularly lead terminal connectors to a corresponding lead electrode grid in sealed lead-acid batteries. Another object of the invention is to provide such new and improved process steps and apparatus wherein a secure electrical contact is made between the desired components without causing any discontinuities or separations in any portions of either part.
It is also an object of the present invention to provide such new and improved process steps and apparatus, which obviates the need for using solders or fluxes.
It is a further object of the invention to provide such new and improved process steps and apparatus, which eliminates the need for moving either welding torch or the cell core while a particular weld is being performed.
It is yet another object of the present invention to provide such new and improved process steps and apparatus, which enable the terminal connector to be retained in place just prior to and during each welding operation.
It is still a further object of the present invention to provide such new and improved process steps and apparatus, which substantially prevent the heat of welding from affecting any other nearby components in the cell core.
It is also another object of the present invention to provide such new and improved process steps and apparatus which enable heat sink means to be conveniently located around the weld target of the workpiece.
Objects and advantages of the invention are set forth in part herein and in part will be appreciated herefrom or may be learned from practice with the invention, the same being realized and attained by means of the steps, and operations as well as the instrumentalities and combinations provided out in the appended claims. Accordingly, the invention resides in the novel steps and processes, and parts, constructions, combinations and improvements herein shown and described.